<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
         * {
            margin: 0;
            padding: 0;
         }
         .box {
            height: 1000px;
            width: 100%;
         }
         .close {
            background-color: black;
         }
    </style>
</head>
<body>
    <div class="box">
         <button class="open">开关灯</button>
    </div>
    <script>
        var box = document.querySelector('.box');
        var open = document.querySelector('.open');
        var flag = 0;
        open.onclick = function() {
           
            if (flag == 0) {
            box.className = 'box close';
            flag++;
            }else {
                box.className = 'box';
                flag--;
            }

        
        }
    </script>
</body>
</html>